﻿<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
<title>无标题文档</title>
</head>
<style>			
  #first{
	   font-size:18px
	}
  #second{
	  font-size:24px  
	}
	#three{
	  font-size:36px	
	}
	
</style>
<body>
	<p id="first">id选择器</p>	<!--在页面定义标记，并自动应用样式-->
    <p id="second">id选择器2</p>
    <p id="three">id选择器3</p>
</body>
</html>
